CBSE Class 10 Science 2019 · Paper 31/2/1 · Question 19

Myopia: a person is considered myopic (near-sighted) when he or she can see nearby objects clearly but cannot see distant (far-away) objects distinctly. Hypermetropia: a person is considered hypermetropic (far-sighted) when he or she can see distant objects clearly but has difficulty in seeing nearby objects distinctly; the near point of the eye is farther away than $25$ cm. Two causes of hypermetropia: (i) the focal length of the eye lens is too long; (ii) the eyeball has become too small. Correction: a hypermetropic eye can focus on the retina only objects at its own near point N′, which is farther than $25$ cm (ray diagram of the near point). Rays from an object at the normal near point N ($25$ cm) would meet behind the retina (ray diagram of the defect). A convex (converging) lens of suitable power placed in front of the eye bends the rays from N so that they appear to come from N′ (ray diagram of the correction); the eye lens then forms the image on the retina. The convex lens thus supplies the additional focusing power needed.